Have any of you guys tried lowering the engine in an GMT800 to get better driveline angles on low trucks? If so, how? I presume an entirely different motor mount would be needed, specifically on the frame side.

Checking my drive line angles, the pinion has to be pointed way up to match the engine/trans. The Ridetech Wishbone doesn't have enough adjustment to pull it up far enough to match the current trans angle. Doing a little geometry, I figure I need to drop the engine 3" and raise the trans 0.5" to get the correct trans to driveshaft angle to set the pinion pretty much flat for 1-1.5 degree working angles on the u-joints. Similar driveshaft angles can be achieved by raising the trans 2.5" for 2-3 degree u-joint working angles. Obviously raising the trans is the easier route but I am not sure the trans can go that high without tunnel interference. I also wonder if the engine could even be lowered 3" due to front crossmember clearance. A low profile oil pan could remedy this and the issue of ground clearance as well. However another benefit of lowering the engine is the lower center of gravity for improved handling. I am basically just thinking out loud here but am curious to any other thoughts our opinions on the subject.

 

What is your rear suspension setup?

 

Ridetech 3-link wishbone system with Viking coilovers.

 

With the wishbone being out of adjustment, I'd call Ridetech and see if they can help. I'd imagine they'd be able to tell you what to change to get your pinion angle in order

 

I could probably make you some mounts that drop it, but 3" is a lot and I bet you would have to modify the frame to do so.

 

If you are just looking for something to piddle on... Check your CAD file for the mounts and see how much you can drop the engine block mount while rotating it forward 3 degrees.

The ultimate goal is to move the engine/trans angle from ~6* down to ~3* to reduce the working angles on ujoints since the pinion is only ~1.5" below the trans now.
Here is a diagram to illustrate what I am working with. White - current configuration, Green - proposed w/engine drop, Yellow - proposed with trans raise, Magenta- straight line reference from axle centerline, each circle at mount locations is 0.5"


I plan to get under the truck this weekend and take some measurements on what can move where and what needs to be modified to do so.

 

I could just cut the holes in little arcs instead so you can clock it how you want it

....as long as the axial center of the engine is at the center of the mount, otherwise it gets more complicated lol

 

I didn't think the engine mounts were symmetrical on the block... so it wouldn't be.

 

Measurements have been taken and dropping the engine is not a viable option without changing the oil pan. The most it could be dropped with a truck oil pan is ~1", if solid mounts were used, due to the steering rack. The front cross brace could be notched in the front but the oil pan would be hanging below the cross brace whatever amount the engine is dropped. This doesn't seem like a very good idea.

There appeared to be a good amount of room in the trans tunnel so I removed the exhaust and was able to raise the trans 2.25" at the trans mount. There is plenty of clearance around the trans to the body but the bell housing is close at the firewall pinch weld where the fuel lines and trans wiring pass thru. This raised the engine/trans angle up 2.8 degrees (6.2->3.4). Its not enough to be equal and opposite to the pinion but I think with placing additional angle on the drive shaft the working angles on the u-joints will be pretty close to equal/opposite. The exhaust has to be modified to clear now so once that is done tomorrow, will check the driveshaft angle and adjust the pinion accordingly.

 

Well... in the words of the infamous BlackGMC... "freaking wasted a day cause I'm a retard" With all the measurements I took, I overlooked one very important clearance... driveshaft to cab. Didn't realize it till I had already cut the exhaust and was trying to fit it back up for the new trans position. With the trans 2.25" up, the driveshaft has interference with the cab. Back at previous height there is only 1.5" clearance from the shaft to cab support. So now it looks like the cab support will need to be notched to get the drive line angles correct.